The immune system of marine mammals and the influence of pollutants have not been adequately investigated and remain in the focus of interest. Each year, several harbor seal pups come ashore on the German Waddensea coast as a natural behavior but also as a result of weakness, potential illness, weather conditions, or human interferences. The immune function especially of newborn seals is not finally understood. During the early postnatal nursing period, immune defense mechanisms are not fully developed, and the immune function especially of newborns is not completely understood. Furthermore, the developing immune system is particularly susceptible to injury from chemical exposure during the perinatal period.
The goal of this study was to investigate alterations in lymphocyte function of harbor seals during the first months of life during their rehabilitation in the Seal Station Friedrichskoog, Germany, and to clarify the immunosuppressive and/or sensitizing influence of metals using a modified lymphocyte transformation test (LTT-MELISA®).
First, we found a strong basal and mitogen-induced lymphocyte response in the newborns, which were often diseased. This indicates a well-developed cellular immunity. The proliferative response decreased in the following months during their rehabilitation in the station. Secondly, the study revealed two different impacts of metals on lymphocytes of newborns. Most of the metals showed an immunosuppressive effect; during their rehabilitation time of three months, the toxic metal effect on the lymphocytes decreased. At the same time, metal hypersensitivities were found in 2 of 15 pups. The sensitizing metals were molybdenum in both seals and, additionally, nickel in one seal.
This study suggests that lymphocytes of newborn seals are highly responsive to mitogens but particularly susceptible to the toxic effects of metals. This effect appears to reverse as the seals become immunologically competent. Older seal pups (1-2 months) can develop metal-specific hypersensitivity reactions. This investigation shows the multiple influences of metals on lymphocytes and indicates a problem of animals living in polluted coastal areas, especially for young pups.